One type of hammer, often referred to as a hammer drill, can have three modes of operation. Such a hammer typically comprises a spindle mounted for rotation within a housing which can be selectively driven by a rotary drive arrangement within the housing. The rotary drive arrangement is driven by a motor also located within the housing. The spindle rotatingly drives a tool holder of the hammer drill which in turn rotatingly drives a cutting tool, such as a drill bit, releaseably secured within it. Within the spindle is generally mounted a piston which can be reciprocatingly driven by a hammer drive mechanism which translates the rotary drive of the motor to a reciprocating drive of the piston. A ram, also slideably mounted within the spindle, forward of the piston, is reciprocatingly driven by the piston due to successive over and under pressures in an air cushion formed within the spindle between the piston and the ram. The ram repeatedly impacts a beat piece slideably located within the spindle forward of the ram, which in turn transfers the forward impacts from the ram to the cutting tool releasably secured, for limited reciprocation, within the tool holder at the front of the hammer drill. A mode change mechanism can selectively engage and disengage the rotary drive to the spindle and/or the reciprocating drive to the piston. The three modes of operation of such a hammer drill are; hammer only mode, where there is only the reciprocating drive to the piston; drill only mode, where there is only the rotary drive to the spindle, and; hammer and drill mode, where there is both the rotary drive to the spindle and reciprocating drive to the piston.
EP1157788 discloses such a hammer.
Another type of hammer only has a hammer only mode and which is more commonly referred to as a chipper. EP1640118 discloses such a chipper.
A third type of hammer will have hammer only mode and hammer and drill mode. GB2115337 discloses such a hammer. In GB2115337, the hammer mechanism comprises a set of ratchets which, when the drill is in hammer and drill mode, ride over each other to create vibrational movement which is superimposed on the rotary movement of the tool holder, thus imparting impacts onto a tool held by the tool holder.
However, all types of hammer will have a hammer mechanism which, when activated, will impart impacts to a cutting tool when held in the tool holder.